1. Field of the Invention
The present invention relates to a classification apparatus for a semiconductor substrate, a classification method of a semiconductor substrate, and a manufacturing method of a semiconductor device suitable for enhancing in-plane uniformity of dry etching.
2. Description of the Related Art
A silicon substrate is made by slicing a single crystal ingot formed by a Czochralski (CZ) method, for example. In the CZ method, oxygen leaking out from a crucible is inevitably mixed at a stage of growth of the crystal. Oxygen in silicon fixes dislocation and increases strength. Additionally, when manufacturing a semiconductor device with using this substrate, oxygen supersaturated at the time of heat treatment in process aggregates to generate precipitate. Oxygen precipitate has a function called gettering, in which oxygen captures a heavy metal atom which is mixed from the outside. As described above, in the silicon substrate made by the CZ method, oxygen which leads to improvement of a yield and characteristic of the device is included, and the method has been widely used since a long time ago.
However, in a crystal grown by the CZ method, there may exist a void defect being an aggregate of atomic vacancies in a crystal growth stage, and when the void defect appears on a surface of the silicon substrate, the void defect may be a crucial defect in an operation of a semiconductor device.
Thus, a method is developed for eliminating the void defect on the surface by means of carrying out annealing to the silicon substrate at a high temperature. In this method, it is utilized that a hole is diffused outward at the time of high-temperature annealing. A substrate made by this method is called an annealed substrate. The annealed substrate is being widely used as a substrate for an advanced device.
The substrates for the advanced device include a substrate called an epitaxial substrate, in addition to the annealed substrate. The epitaxial substrate is a substrate in which a silicon thin film is epitaxially grown on a silicon substrate made by the CZ method. Even if the void defect exists on a surface of the substrate made by the CZ method, a silicon atom at the time of epitaxial growth is filled in the void defect. Therefore, the void defect is eliminated also in the epitaxial substrate.
As described above, primarily three kinds of substrate exist as the silicon substrates.
Additionally, when manufacturing a semiconductor device by using such a silicon substrate, a semiconductor film, an insulating film and a conductive film are formed, and these films are processed. Processing methods of these films are classified primarily into dry etching and wet etching.
However, recently, variation increasingly occurs in etching speed even in the same substrate at the time of dry etching. In other words, though etching conditions such as a pressure in a chamber and an applied voltage are the same, there occurs variation in etching speed. Along with the variation of the etching speeds, variation occurs in line width of the formed pattern. As a consequence, variation occurs in characteristic among semiconductor devices manufactured from the same substrate. For example, threshold voltages of transistors may vary by variation of gate widths. However, a cause of the variation has not been revealed yet.
Related arts are disclosed in Japanese Patent Application Laid-open No. 2001-156152, and Japanese Patent Application Laid-open No. 2001-297957.